The present invention relates to a method of and an apparatus for producing methanol.
Methods and apparatuses for conversion of methane into methanol are known. It is known to carry out a vapor-phase conversion of methane into a synthesis gas (mixture of CO and H2) with its subsequent catalytic conversion into methanol as disclosed, for example, in Karavaev M. M., Leonov B. E., et al “Technology of Synthetic Methanol”, Moscow, “Chemistry” 1984, pages 72–125. However, in order to realize this process it is necessary to provide a complicated equipment, to satisfy high requirements to purity of gas, to spend high quantities of energy for obtaining the synthesis gas and for its purification, to have a significant number of intermittent stages from the process. Also, for medium and small enterprises with the capacity less than 2000 t/day it is not efficient.
A method for producing methanol is also known which includes a separate supply of a hydrocarbon-containing gas heated to 200–500° C. under pressure 2.15 MPa and an oxygen-containing gas in a mixing chamber, subsequent stages of incomplete oxidation of methane with a concentration of oxygen 1–4 volume percent with an additional introduction of reagents (metal oxide catalyst, higher gaseous hydrocarbons or oxygen-containing compositions, a cold oxidizer) into the reaction zone of a reactor, cooling of the reaction mixture in a heat exchanger, separation of methanol from liquid reaction products in a separator, supply of gaseous waste products to an input of the reactor as disclosed in the Russian patent no. 2,049,086. However, this method requires the use of a catalyst or additional reagents and an intense heating of the reacting gasses, which leads to a decrease of methanol yield and to an increased possibility of soot formation.
A further method of producing methanol is known, which includes a separate supply into a mixer of a hydrocarbon-containing gas (natural gas typically) and an oxygen-containing gas (air or oxygen). This mixture a subsequently supplied into a non-cathalytic reactor for gas phase incomplete oxidation at pressures of 1–10 MPa during up to 1000 seconds at a temperature 300–500° C. without catalyst, return of waste reaction gasses which contain non-reacted methane for mixing with the initial hydrocarbon-containing gas into the first reactor or into the second reactor (which is connected in series with the first reactor), as disclosed in the British patent document GB 2,196,335A. This method provides a high yield of methanol. However, due to significant time of reaction and relatively low per pass conversion (5–15% of methane can reacts during each passage through the reactor) this method has a low efficiency.
A further method of producing methanol by a separate supply and oxidation of hydrocarbon-containing gas and oxygen-containing gas at temperature 370–450° C. and pressure 5–10 MPa and time of contact in the reactor 0.2–0.22 sec is also known, and includes cooling of the heated reaction mixture to 330–340° C., introduction of methanol into the reactor, as disclosed in the patent document of the Soviet Union SU 1,469,788. Cooling of the reaction mixture without intermediate condensation and separation to 380–400° C. in multi-stage heat exchangers arranged in the reactor with subsequent supply of the mixture to 2–3 successive stages of oxidation is disclosed in the patent document of the Soviet Union 1,336,471. In the first case it is necessary to have an additional consumption and a secondary separation of methanol that leads to unavoidable losses, and in the second case it is necessary to provide additional cooling loops with circulation of additional cooling agent in them.
An apparatus for producing methanol is known, which includes a plurality of units arranged after one another and connected by pipes, in particular a mixing chamber connected to separate sources of hydrocarbon-containing gas and air or oxygen, a reactor composed of an inert material with a heating element for incomplete oxidation of methane in a mixture supplied into the reactor under an excessive pressure, a condensor and a separator for separation of methanol from the products of reaction, a vessel for recirculated gaseous reaction products with a pipe for their supply into the initial hydrocarbon-containing gas or mixing chamber as disclosed in the British patent no. 2,196,335A. However, a significant time of presence of the reagents in the reactor reduces efficiency of the apparatus, and makes the process practically unacceptable in industrial conditions.
An apparatus which is close to the present invention is disclosed in Russian patent no. 2,162,460. It includes a source of hydrocarbon-containing gas, a compressor and a heater for compression and heating of gas, a source of oxygen-containing gas with a compressor. It further includes successively arranged reactors with alternating mixing and reaction zones and means to supply the hydrocarbon-containing gas into a first mixing zone of the reactor and the oxygen-containing zone into each mixing zone, a recuperative heat exchanger for cooling of the reaction mixture through a wall by a stream of cold hydrocarbon-containing gas of the heated hydrocarbon-containing gas into a heater, a cooler-condenser, a separator for separation of waste gasses and liquid products with a subsequent separation of methanol, a pipeline for supply of the waste gas into the initial hydrocarbon-containing gas, and a pipeline for supply of waste oxygen-containing products into the first mixing zone of the reactor.
In this apparatus however it is not possible to provide a fast withdrawal of heat of high-thermic volume reaction of oxidation of the hydrocarbon-containing gas, because of inherent limitations of the heat-exchanger. This leads to the necessity to reduce the quantity of supplied hydrocarbon-containing gas and, further it reduces the degree of conversion of the hydrocarbon-containing gas. Moreover, even with the use of oxygen as an oxidizer, it is not possible to provide an efficient recirculation of the hydrocarbon-containing gas due to fast increase of concentration of carbon oxides in it. A significant part of the supplied oxygen is wasted for oxidation of CO into CO2, which additionally reduces the degree of conversion of the initial hydrocarbon-containing gas and provides a further overheating of the reaction mixture. The apparatus also requires burning of an additional quantity of the initial hydrocarbon-containing gas in order to provide a stage of rectification of liquid products with vapor. Since it is necessary to cool the gas-liquid mixture after each reactor for separation of liquid products and subsequent heating before a next reactor, the apparatus is substantially complicated, the number of units is increased, and an additional energy is wasted.
A further method and apparatus for producing methanol is disclosed in the patent document RU 2,200,731, in which compressed heated hydrocarbon-containing gas and compressed oxygen-containing gas are introduced into mixing zones of successively arranged reactors, and the reaction is performed with a controlled heat pick-up by cooling of the reaction mixture with water condensate so that steam is obtained, and a degree of cooling of the reaction mixture is regulated by parameters of escaping steam, which is used in liquid product rectification stage.
Other patent documents such as U.S. Pat. Nos. 2,196,188; 2,722,553; 4,152,407; 4,243,613; 4,530,826; 5,177,279; 5,959,168 and International Publication WO 96/06901 discloses further solutions for transformation of hydrocarbons.
It is believed that the existing methods and apparatus for producing methanol can be further improved.